def lone_sum(a, b, c):
  if a!=b and b!=c and a!=c:
    return (a+b+c)
  if a==b==c:
    return (0)
  if a!=b and b==c and a!=c:
    return(a)
  if c!=a and c!=b and c!=a:
    return (c)
  if a==c and b!=c and b!=a:
    return (b)